Waterproofing of Roof With Discarded Tyre Rubber Crumb

By
Kaushal Kishore, Materials Engineer, Roorkee

INTRODUCTION :
About one crore 10 lakhs all types of new vehicles are added each year to the Indian roads. The increase of about three crores discarded tyres each year pose a potential threat to the environment. Tyres are recycle yet significant number are added to existing tyre dumps or landfills. The generation of waste tyres far exceeds than now being recycle. Waste rubber tyres cause serious environment problems all over the world. This accumulated waste materials can be used in Civil Engineering Construction.

Early studies on the use of worn out tyres in asphalt mixes were very promising, not much attention has been given to the use of rubber from scrap tyres in portland cement concrete. So far no research has been done in the use of rubber crumb for RCC and RB roof slab water proofing.

TYRE CRUMB:
Crumb rubber may be produced by an ambient process (mechanical sizing) or by cryogenic process (freezing). In the mechanical process, tyres are reduced to chips or shreds and then put through granulators which separate and remove loose steel and fiber and further reduce rubber particle size. Finally, the small rubber chunks are ground to produce rubber crumb of 30 to 80 mesh size. In the cryogenic process, tyre chips are frozen in liquid nitrogen as they pass through a cryogenic tunnel then broken down by impact. They then pass through a series of screen meshes where they are shattered into their three component parts: rubber, steel and fabric. Although the cryogenic process is the more expensive of the two, it produces smoother and smaller crumb.

PROPERTIES OF TYRE RUBBER:
a) Density : Tyres are slightly heavier than water and will sink in water unless entrapped air provides enough buoyancy to allow them to float. This generally occurs only with whole tyres or fine crumb rubber.

b) Moisture absorption: Tyres and shreds can trap water on the surface and in irregular contours, but they are relatively impervious to actual absorption. Various studies cited in ASTM D 6270-98 indicate maximum moisture absorption of 2-4%.

c) Thermal Insulation: Rubber is a poor thermal conductor, conversely providing a better thermal insulation than soil or aggregate.

d) Acoustic Insulation: Tyre rubber is a poor acoustic conductor and, therefore a good insulator.

e) Temperature Tolerance: Tyre rubber is capable of withstanding a full range of ambient temperature extremes without undergoing permanent property change. Some properties like flexibility change as a function of temperature, but the change is reversible and repeatable.

f) Leaching Characteristic: Tyre shred leaching characteristic have been examined under a wide range of pH conditions. Extensive practical experience has conformed the absence of any deleterious impact.

g) Flammability: Tyres shreds have a reported flash point of 3060C, higher than some other building materials used for Architectural purposes such as wood, paper, foam, and fabric. When crumb rubber is combined with cement and sand, this may control the flammability of the resulting product.

PROPERTIES OF RUBCRETE MIXTURE:
Cement, aggregates, rubber and water mixture having all good properties it has a draw back of lower strength due to its poor bonding with concrete matrix. In the present study this draw back some what has been overcome by the addition of specially formulated additives.

In the early study it was found that coarse grading of rubber granules lowered the compressive strength of rubber mixtures more than fine grading. There was about 85% reduction in compressive strength and 50% reduction in tensile strength when the coarse aggregate was fully replaced by coarse rubber chips. However, specimen lost upto 65% of their compressive strength and upto 50% of their tensile strength when the fine aggregate was fully replaced by fine crumb rubber. The rougher the rubber particles used in concrete mixture the better the bonding they develop with surrounding matrix and, therefore, the higher the compressive strength achieved. If the bond between rubber particles and the surrounding cement paste is improved, then significantly higher compressive strength of rubcrete mixtures could be obtained. The following are the possible causes in strength reduction of rubcrete mixtures:

a) The rubber is much softer than the surrounding cement paste, upon loading cracks are initiated quickly around the rubber particles due to this elastic mismatch, which propagate to bring about failure of the rubber-cement matrix.

b) Weak bonding between the rubber particles and the cement paste in creases void, resulting reduction in strength.

c) Strength of concrete depends mainly on the density, size, and hardness of coarse aggregate. When aggregates are replaced with light, flexible, and smooth surface rubber a reduction in strength is anticipated.

While in structural concrete strength is one of the important factor. However, for non-structural concrete such as roof top rending for insulation and water proofing rubber mixture may be suitable material, as it has a property of insulation and also flexibility due to which it is not cracked in the movement of slab accordingly suitable for water proofing. Where as in due course of time cement-sand rending crack even when mixed with polymers, and the leakage of water started again. In the present study this has to be seen that when rubber mixture as rending applied on crack roof surface in the number of natural roof movement cycle this should not be cracked, and cost wise it should be near about equal to conventional roof treatment const.

EXPERIMENTAL WORK:
Materials:
1. Cement : OPC 43 Grade conforming to IS: 8112-1989
2. River Sand : The properties of sand is given in table-1.
3. Crumb Rubber : Many factories in India are manufacturing crumb rubber, in this study crumb rubber was obtained from local dealer. Its properlties are also given in Table-1.

MIX DESIGN:
After many trials and testing, with the given set of materials three mixes are finalized the details of which are given in table-2.

Mix No. 1 is well known and it is not used in the rending. Mix No. 2 has shown lower strength accordingly this is also not used in this study. Mix No. 3 found satisfactory in all respect hence used as final mix in this study.

ROOF TOP RENDING FOR WATER PROOFING AND INSULATION:
A leaking and cracked RCC roof selected for this study. Mortar of No. 3 at a thickness layer of 25 mm applied upon this roof. Cleaning of roof, preparation of given mortar, laying finishing and curing was done as specified in various litarture/codes. After completion of curing cycle, the roof is left to dry. It was then filled with water for 3 days. It was again left to be dry and then filled with water. After 3 cycles, the roof was left to be dry for considerable time. It was then filled with water for 3 days. On the third day the roof was inspected for any leakage. No leakage was observed. The roof was again left to be dry for considerable time and then inspected for any cracks. No crack was observed

DISCUSSIONS :
1. The given treatment with rubber crumb found to be satisfactory for water proofing and insulation.
2. Long performance beyond one year is to be observed.
3. The cost of this treatment comes to about Rs. 29/- per sq. ft.
4. CAUTION: No fixed mix design can be worked out for this treatment. Mix design is to be worked out with the given set of site materials, roof and site conditions.
5. Advantage of this treatment:

a) Utilization of waste material.
b) All materials are easily available.
c) Having lower density, it reduces load on roof.
d) Flexible materials which does not crack.
e) Treatment cost is about Rs. 29/- per Sq.Ft including labour, which can further reduced if materials are purchase in bulk.

CONCLUSION:
Further, research work is in progress for the final conclusion.
Table- 1: Properties of materials:

I.S. Sive size	Percentage passing by mass
	Sand used in the Mix	Rubber crumb used in the Mix	Sand for masonary mortar as per IS: 2116-1980
4.75	100	—	100
2.36 mm	100	—	90-100
1.18 mm	80	100	70-100
600 Micron	56	100	40-100
300 Micron	18	82	5-70
150 Micron	3	74	0-15
Specific Gravity	2.65	1.14	—
Bulk Density room dry as filled loose in measuring boxes (kg/lit)	1.62	0.36	—

Table-2: Mix Design details of rending mortar:

Materials	Mix-1 Control	Mix-2 Only Rubber	Mix-3 Rubber + Admixture
OPC 43 Grade (gm)	700	700	700
River Sand (gm)	1750	1225	1225
Rubber Crumb (gm)	—	227	227
Admixture Added	NIL	NIL	Yes
W/C Ratio	0.6	0.6	0.6
Workability (Observed Practical)	Good	Fair	Good
Average Weight of 100x100x100 mm SSD Cubes (gm)	2181	1816	1810
Average, 7 days Compressive Strength of SSD Cubes (N/mm2)	7.2	2.7	4.1

Note: Proportions by weight can be converted to proportion by volulme, by dividing with the bulk density of the materials available for use at site. The bulk density of OPC may be taken 1.44 kg/lit.

REFERENCES:
1. I.S. : 383-1970 : Specification for coarse and fine aggregates from natural sources for concrete (second revision), BIS, New Delhi
2. I.S : 2116-1980 : Specification for sand for Masonry Mortars (First Revision) BIS, New Delhi.
3. IS : 8112-1989 : Specification for 43 grade ordinary portland cement (First Revision)
4. ASTM D 6270-98 : Standard Practice for use of Scrap tires in Civil Engineering Application.
5. ASTM D 5644-01 : Standard Test Method for rubber compound Materials- Determination of particle size distribution of vulcanized particle rubber.
6. Khatib, Z.K. And Bayomy, F.M. “Rubberized Portland Cement Concrete” Journal of Materials in Civil Engineering pp. 206, 213, August 1999.

We at engineeringcivil.com are thankful to Sir Kaushal Kishore for submitting his research paper on “Waterproofing of Roof With Discarded Tyre Rubber Crumb” to us. We are sure this will help engineers understand how waterproofing can be done by using the waste material which is beneficial not only economically but financially also.

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